1. Field of the Invention
The present invention relates generally to a preterminated fiber optic distribution cable and, more particularly, to a fiber optic distribution cable having at least one predetermined access location for providing access to at least one preterminated optical fiber.
2. Description of the Related Art
Optical fibers are used for a variety of applications including voice communication, data transmission and the like. With the ever-increasing need for connecting remote locations to a fiber optic distribution cable, it is apparent that more efficient methods of performing a mid-span access of a distribution cable are required. Typically, to perform a mid-span access, a technician must remove a portion of the cable sheath in the field at a convenient location along an installed distribution cable. Once the sheath is removed, the technician must access pre-selected optical fibers, sever the pre-selected optical fibers and remove a length of the optical fibers from the distribution cable. The removed length of optical fiber provides the field technician with adequate length to splice one or more optical fibers of a cable comprising a lesser amount of optical fibers than the distribution cable, typically termed a “drop cable,” to the distribution cable optical fibers. After all splicing is complete, the accessed location is typically covered using an enclosure designed to protect the splices and the exposed section of the distribution cable. This time consuming process is typically accomplished by a highly skilled field technician at a significant cost and under less than ideal working conditions.
Several approaches have been developed to overcome the disadvantages of accessing optical fibers in the field. In one approach, the splicing of drop cables to the distribution cable is performed at a factory during the manufacturing of the cable. The preterminated cable, including the main cable, drop cables and associated splice closures, are assembled and wound onto a cable reel to be delivered to an installation site. Accordingly, conditions for making high quality splices may be maximized in the factory, thereby increasing splice quality and also reducing the expense and difficulty associated with field splicing.
In one approach, U.S. Pat. No. 5,121,458 (the '458 patent) issued to Nilsson et al. and entitled “Preterminated Fiber Optic Cable,” describes a preterminated optical fiber cable having a main trunk cable comprising a plurality of optical fibers disposed therein, and multiple drop cables spliced to the trunk cable at various branch points. The preterminated fiber optic cable is completely assembled at the time of manufacture and is easily installed thereafter. At each branch point, a splice closure is utilized for protecting the optical fibers and splices from moisture and mechanical damage, providing a strong anchoring point for the optical fiber drop cable and insuring that the minimum fiber bend radius is not violated. While the preterminated fiber optic cable assembly described in the '458 patent is useful in certain applications, its use is limited to applications in which it is installed through a conduit having an outer diameter of about 4 inches or greater. In addition, the relatively large outer diameter of the splice closure may greatly hamper the winding of the assembled cable onto a cable reel. The large diameter of the splice closure may prevent installation of the cable within a section of buried conduit, which typically has a diameter of less than about 1.9 inches, and in some applications less than about 1.25 inches. For example, conduits having a diameter of less than about 1.25 inches are commonly used for placing fiber optic cable under obstructions, such as driveways.
In another approach, U.S. Pat. No. 5,528,718 (the '718 patent) issued to Ray et al. and entitled “Fiber Optic Cable System Including Main and Drop Cables and Associated Fabrication Method,” describes an approach to overcome the difficulties in reducing the size of the branching point of the drop cables from the main cable. The cable system is assembled in the factory and includes a main cable and one or more drop cables connected to the main cable at spaced apart locations along the main cable. The drop cable is spliced to the main cable using a splice closure including a fiber guide that secures spliced together end portions of the respective optical fibers in a longitudinally extending direction and devoid of any slack coils of optical fiber. Accordingly, the overall diameter of the splice closure is reduced in size as compared to the system of the '458 patent, thereby permitting the cable system to be stored on a reel and to be readily placed within relatively small diameter conduits. The '718 patent describes applications in which the fiber optic cable system may be employed in conduits having a diameter of about 1.8 inches. While the outer diameter of the '718 fiber optic cable system represents a decrease in size compared to the '458 preterminated fiber optic cable diameter, it is still desirable to produce a cable system having a diameter less than about 1.25 inches.
Accordingly, it would be desirable to produce a preterminated fiber optic distribution cable having one or more predetermined access locations with factory preterminated optical fibers along a length of the distribution cable, while achieving the lowest profile possible and still maintaining discrete fiber capability. It would also be desirable to provide a preterminated fiber optic distribution cable having one or more low profile access locations suited for both buried and aerial installations. With regard to buried installations, it would be desirable to be able to pull the distribution cable through a conduit having a diameter less than about 1.9 inches, and more preferably, less than about 1.25 inches, such as a bore or conduit underneath a driveway.